1. Field of the Invention
This invention relates to a cogeneration system provided with a plurality of generators with respect to an engine.
2. Description of the Prior Art
A conventional large-sized generator driven by an engine comprises mostly an induction machine. When an induction machine is used in a generator, a generated voltage can be set constant easily by controlling the input exciting power even if the rotational frequency varies. Accordingly, such a generator generally comprises an induction machine. A generator or a motor in which a permanent magnet is used as a rotor has characteristics that it has a high level of output and a simple construction, so that it has recently come to be used in large quantities for industrial machines and tools.
However, in a generator, a voltage increases as the rotational frequency thereof increases, and setting the voltage constant is therefore difficult, so that a complicated control apparatus is required. Regarding a rotor in a generator, the rotational frequency thereof increases as the voltage and amperage increase, and, consequently, a large centrifugal force occurs in the rotor. It is necessary that the rotor withstands such a centrifugal force. Therefore, a rotor is generally formed so as to withstand a centrifugal force by fitting a reinforcing ring around an outer circumference of a permanent magnet which constitutes the rotor.
The known generator using a permanent magnet as a rotor include, for example, the miniaturized generator disclosed in Japanese Utility Model Laid-Open No. 146975/1990, the dynamo-electric machine generator disclosed in Japanese Utility Model Laid-Open No. 162977/1985 and the permanent magnet type rotary machine disclosed in Japanese Patent Laid-Open No. 272850/1987.
For example, in the miniaturized generator disclosed in Japanese Utility Model Laid-Open No. 146975/1990, a main shaft and a rotor are connected together via a governor mechanism in which a governor weight is supported pivotably on a pair of links, the governor weight being displaced from the main shaft by a centrifugal force in accordance with a rotational frequency of the main shaft to reduce an angle between the links, whereby the rotor is moved in the direction in which the rotor gets out of a stator.
The high-output AC generator disclosed in Japanese Patent Laid-Open No. 236260/1995 is adapted to control a generation power properly by controlling a magnetic flux density in accordance with a rotation speed. In this generator, a control ring is provided relatively rotatably between a rotor and a stator, and a permeable member which can be engaged with and disengaged from the control ring.
In order to produce a cylindrical permanent magnet by a regularly used method, alloy powder containing elements, such as iron, neodymium, samarium and cobalt is packed in a cylindrical mold comprising a nonmagnetic material, and the alloy powder is compression molded and solidified at a high temperature, a molded body thus obtained being sintered instantaneously with high-frequency heat. During the sintering of the molded body, the NS poles are set, i.e., the magnetic lines of force in the alloy are set by applying a magnetic force thereto. A cylindrical sintered body of a permanent magnet is then taken out from the sintering mold, and the outer and inter circumferential surfaces of the sintered body are ground to make a sintered body of a permanent magnet. On the other hand, a thin-walled outer cylinder formed by winding up elongated carbon fibers is prepared as a member for reinforcing the sintered body. The sintered body of a permanent magnet is then press-fitted in the thin-walled outer cylinder by a press to finish a rotor.
In a generator using a permanent magnet as a rotor, a generated output level is a product of a rotation speed of the rotor and the magnetic field strength. Accordingly, a generated output level increases in proportion to the rotation speed of the rotor. However, it is difficult to increase a generated output level by forming a rotor of a large diameter of a permanent magnet, and thereby increasing a peripheral speed thereof. Namely, as far as a rotor comprising a permanent magnet is employed, the generation of a large output is difficult.
When a rotor is formed by mounting a permanent magnet on an outer circumference of a flywheel, which is mounted on an output end of an engine, with a shaft of the flywheel used as a rotary shaft of the rotor, the permanent magnet becomes large, and a stator necessarily has a large diameter, so that the dimensions of the generator increases. Namely, the diameter of the generator becomes too large, and the generator cannot be installed in certain places. A system for supplying electric power of a high efficiency by using a ceramic insulating turbo compound engine constitutes a very effective system as a power source for an urban area but installing such a system on a roof top or in a basement of a building has also to be taken into consideration. Since the spaces in such places for the installation of this system involve severe conditions, it is demanded that the system be formed to a compact and low-noise structure.
In a generator in which a rotor revolving at a high speed is formed by using a permanent magnet, the powder of an iron-neodymium alloy is sintered, and the resultant sintered body is shaped to a predetermined form and set to a predetermined precision for producing this permanent magnet, in many cases. When a rotor in a generator is rotated at a high speed, a large centrifugal force is exerted thereon. Consequently, it is demanded that a permanent magnet constantly has a strength high enough to prevent the permanent magnet constantly has a strength high enough to prevent the permanent magnet from being bursted by the centrifugal force thereof. Moreover, it is necessary to increase the strength of a permanent magnet in proportion to the dimensions of an object rotor. However, in order to produce a permanent correspondingly to the dimensions of an object rotor, a generator of a high cost is produced, which necessarily poses an issue of how to reduce manufacturing cost.